A XPropMatch consists of a list of conditions and function telling what to do.

The list entries are pairs of an XProperty to match on (like wM_CLASS, wM_NAME)^1,
and an function which matches onto the value of the property (represented as a List
of Strings).

If a match succeeds the function is called immediately, can perform any action and then return
a function to apply in windows (see Operations.hs). So if the action does only work on the
WindowSet use just 'pmP function'.

*1 You can get the available properties of an application with the xprop utility. STRING properties
should work fine. Others might not work.